Recovery of ammonia from ore tailings pulp



Jan. 11, 1949.

R. R. FITzHUGH Erm.

RECOVERY OF AMMONIA rFROM ORE TAILNGS'PULP Y Filed oct. '7, 194s ORE TAIL/NGS PULP QEcYcLE OEE .SLL/APR Y ORE o/sc/-m eef QECYCLE OPE SLUQIZY OPE TAIL/NGS PULP PETENT/ON K HEAT/NG PE C YC L E ORE SLUEPY I BY ATORNEYs Patented Jan'. 11, 1949 RECOVERY OF AMMONIA FROM ORE 'I AILINGS PULP Robert R. Fitzhugh, Nicaro, Cuba, and Benjamin F. Frederick and Bernard A. Axelrad, Freeport, Tex., assignors to Nicaro Nickelk Company, New York, N. Y., ay corporation of Delaware y Application October 7, 1943, Serial No. 505,402

l. This invention lies inthe field of metal recoveryfrom nickeliferous and other ores and relates specifically to methods of recovering residual'ammonia contained `in tailings pulps from which the nickel, copper, cobalt or other metal content has been leachedV by means of an ammoniacalleachingsolution;v

In a patent application filed by our associate, Robert'C. Hills, SerialNo. 467,559, led December l1.1942, new Patent No. 2,400,114,113 process of recovering nickel from various ores is described involving crushing the ore to a nely divided state, roasting and cooling it in a reducing atmosphere, leaching out the niclel content with an ammoniacal solution during aeration and separating the nickel from the leaching solution. Recovery of the residual nickel and ammonia in the ore tailings pulp, to which prob-v lem they prior application is particularly directed, is described therein as being accomplished by washing the spent ore with fresh `leachingso lution or other ammoniacal solution of a sufriciently high concentration to prevent thnickel content, from precipitating out and then-recovering the ammonia of the ammoniaca] solution retained in the tailings pulp by passing the pulp through' a plate tower wherein the ammonia' is distilled ofi with the aid of direct steam.

This ammonia distillation process is described more in detail in said lprior specification as preferably involving pumping the ore tailings pulp into the top'of a multiplate distillation tower from which it passes to the bottom of the tower in countercurrent movement to a supply of steam introduced at the' bottom of the tower..I "Concentrated ammonia vapors are disclosed to pass out of the top of the tower where theyl may be condensed and collected inconventionalv apparatus, and the spent ore slurry containing only a small amount of the original ammonia content is said to-be discharged to waste from the bottom of the tower.

Operation of this ammonia recovery process in conventional plate towers has been found by the present applicants to involve difficulties dueto deposition of a scale on the surfaces of the top plates which prevents continuous or uninter-y rupted operation. An examination and analysis oi this scale revealed that it is composed of a mixture of magnesium compounds and fine particles of ore. Apparently its presence is due to the existence of magnesium impurities in the `initial ore treated and to the presence of a complex salt, ammonium magnesium carbonate, in the spent ore tailings, which Isalt is dissolved during the initial heating in the 'plate tower.

1o claims. (orcs-14193) i* Upon further heating of the pulp on 'the top plates of the tower, the complex magnesium ammonium carbonate hydrolyzes and precipitates the magnesium apparently inthe form ofk its hydroxide or itscarbonate. Since the `deposition of the f` scale has been found to occur wherever heat is transferred to the pulp, such as at vapor nozzles, bubble caps and the topsides of the plates, it is evident that the transfer of heat to the pulp from hot surfaces during hydrolysisis at least in part f the cause of the formation ofthe scale..

In accordance with a preferred process of the present invention and following the foregoing discoveries, the deposition of the scale is .prevented by accomplishing all or'part of the heat treatment of the ore` tailings pulp by direct transfer from a heated fluid or huids, This heating operation is effectively andfeconomically carried out in accordancewith the present invention by recycling hot ore tailings slurry from which the unstable `magnesium compoundsfhave already been removed as by l1. recipita"i',ion and also separation, if 'so desired. lThe introduction of the hot recycled slurry into the ore tailings pulp to' be treated also `has the benecialresult and advantage of slowing down the rate of precipitation of `the magnesium compounds by dilution effect. Dilution of the magnesium concentration in the pulp liquor to a point at or below about .02,gram per A100 cc.has been found to prevent excessive deposition of scale. Instead of adhering to the surfaces'of 'the' plates ofthe ammonia stripping column, the magnesium compounds appear to deposit on the hot ore particles.

" In one embodiment Aof the invention, ore tailings pulp containing the ammonia solution to be recovered and .05 to .11 gramof combined magnesium per 100 cc. of liquor is introduced'into an auxiliary tank to which is added a quantity of hot recycled ore slurry from` which the ammonia content has been recovered in a previous run of the process. The mixture is further heated in the tank,` preferably by means of "direct steam, and is retained therein untill the magnesium content has for the most part precipitated out on Supplemental mechaninecessary to prevent settling and deposition. Thereupon the pulp,vfreed of unstable magnesium compounds, is withdrawn and is then introduced into the hereinbefore mentioned ammonia stripping tower wherein it is deprived'of its ammonia content in accordance with the process' of said prior application.r Since thefmagneslum compounds are no longer present in anunf stable form, little or 'no depostionoi magnesium occurs on the surfaces of the plates, and the ammonia stripping operation in the tower may be continued for long periods of time without interruption.

Since the conversion of the soluble magnesium compounds' into fthe insoluble magnesium com.- pounds is aA time reaction, theperiod'l during which the mixture of ore tailings pulp containing the ammonia solution to be recovered and the spent ore slurry is retained iny the. tank. should-1` be correlated with the temperature maintained.

in the'tank. If the temperature is maintained at 170-1'5 F., a period of heatingof"twenty-minutes is usually suilicient. If' a: higher tempera.-

ture of 190 F. or above is employedpseven. to.

ten minutes is generally sufficient.

The ratio of ore tailings slurry-.to thelammonia.- containing ore tailings pulp may be varied considerably, a ratio of 2:1, giving good results with the type of ore of thenature hereinbefore described; Ratios asflow'as 1':1` and as high as 5:1 may be employed, however; Theratio preferredA in any particular operation of'the'process depends upon thel quantity oiimagnesium impurities pres'- ent'and upon thev'temperature to'beobtained in the feed pulp fromthe recyclestock. Thelarger the amount ofirecycled" ore `tailings slurry employed;the lessertheamountof steam heat requiredin'they heating `zon-ev to` completethev hydrolysis ofA the solubleV` magnesium compounds. The spent ore-tailings'slurry is. most economically employed at the temperature itl isobtained'l in the process; for if. it"l is permitted. to cool, additional steamis requiredto raise its temperature and the temperatureof the'initial ore tailings y.pulp to a heightat whichthe hydrolysis. will voccur in a reasonable period of` time.

In asecond embodiment of ithe invention, a portion of the spent hot'ore slurry is recycled andintroduced directly into the'ammonia. strippingl column near the top thereof .at such point .that it mixes with the oretailings pulp containing the ammonia solution to be recovered when-,thelatter isata temperatureof-somewhat.less than 15071?. Deposition of magnesium compounds onv the equipment is preventedby eiectingthe hydrolysis ofthe soluble.magnesiumcompoundsfin ,the presence ofhot ore particles,. by the. dilutioneffect of the addedsl'urry, and'lby theincrease.invelocity and abrasive; effect of thei oreparticles passing. through.. Since` thisembodiment does.` not sep.- arate the. functions of scale prevention. and am.-V monia stripping, more .careful regulation of vcon-- ditions. in the. ammonia.. stripping. tower is required. It has the economic advantage, however, in not requiring livesteam atthepointwhere the precipitation takes place nor an additional-amount of. steam in the column.

In. accordancefwith a thirdand preferred .embodimentof theV invention, recycled ore-slurry obtained` as hereafter described isxintroduced to.- gether with-.ore tailings pulpwcontaining; ammoniaat the topvof an auxiliary, heatingv tower con.- taining several platesi- In thei-heatingtower, .the temperature ofthemixtureis-raised by; the coun-,- tercurrent'vflow of the .lV-ammoniafigases` and vapor flowing from the.- ammonia"v stripping` column', which gasesare-introduced into the bottom of the heatingftower andiromwhich .they pass .out `at the top thereof. The heated :mixture of pulp;- and slurry-1 isf then passed ,tof an': auxiliary-1 retention tankwhereinthe sameis retained. until: hydrolysis oi the soluble `magnesium compounds has taken place. Partofthe.v mixture thus-obtainedisrecycled and .introducedintoethe top ofiheiauxiliary,

heating tower as hereinbefore described. The remainder of the mixture is then passed to the top of the ammonia stripping column through which it ows in countercurrent to a supply of steam which volatilizes the ammonia. The ammonia and; the. spenti steami or. vapor. passes through'y the heating column and "thence to a recovery system.

This third embodiment is of particular advantage'fortherreason that the sensible heat of the ammonia gases and vapor is utilized in the preheating. tower. TheV4 use of the plate heating tower; andin'particul'ar one of the dish-tray type,

isof amaterial'advantage in that the low pressure ofithe ammonia-.gases and vapor as obtained from the ammonia stripping column is suiiicient to forceA itsway-'through the heating tower in contact with the pulp and slurry flowing therethrough in countercurrent. If the heating were effected-in an ordinary tank of high pressure drop such-as employed in. the first'. embodiment describecLherein, diculty or extraexpense would beencounteredin forcing thegases through the tailingsl In atypicalrun oithisthird embodiment, the ore tailings pulp containing, the ammonia to be recovered. isintroducedlintoithe heating tower ai; atemperature of.fabout.120 and the recycled slurry atta temperature of about F; The ratio. of the.- latter tothe former. ismaintainedat. about 2:1.. Themixture at the -top of the` tower under these conditions wouldhave` a temperatureof about .1709 In passingthrough the heatingtow-er,.the-temperature of. the mixture israised tofabout19'0. E. Themixtureisretained in they retention'tank for about twenty minutes, after-which .it is-'dividpart of which is :recycled: and: thev other. part .of ,which is -led to the 4ammonia. stripping column.

Drawings are includediherewith to illustrate apparatuses in which the.- various embodiments of'thefinvention may-be.carried.out.` It should he understood-r, however, that :the invention is not limitedtozanyspecic details ofconstruction and th'atit'mayfbe practiced inother apparatus exceptwhere otherwise-indicated herein. The -iigures are diagrammatic in'characterVv and conse'- quentlyfdo not. show: many `conventional. details of construction,- valves; and :the like, required-.for actual operation.-

With.reference-1to-Figure'fL illustrating an -apparatus in whichrthe -i'stiembodiment of'thevin: ventionrnaygbecarrieckout, there ris. an ammonium strippingtowerr I 0'.: havin-ge a :series of conventional plates 1 I If arranged: therei-rrzin they usuallmanner: At the;top;:of the=towerJtherefis provided an inlet" I2- for" the-:introduction: of fa mixture of ore tailingspulp. containing ammonia to be recovered, with' recycled'slurry.J outlet I3f` is also providedz-ats thez'top. of` thectowerf fortthe-outward passage of ammonia gases and vapor, whichv passage leadsto af conventional 'ammonia recovery apparatussmotshoWn). Near thebottom of the tower,` there are-provided aconduit I4 for the introduction of live steamandan' ore discharge conduit-l I5; conduit I5" contains a branch vali/ed! conduit I 6"leading toa. heater retention tank I'I. This tankll is providedwithan agitate ingmeans I'Ia,..an inlet I8I ior introducing ore tailings pulp` containing-ammonia. to be-recovered, a -live steam inletv conduit I9.. and; ansoutlet con-V duit fforfzthe fmixturefoi' the=recy`cled oreslurry andxtheJI ore tailingsxipulo. This. conduit 20v-iconnectsthroughthe pumpyZI With-.theiinlet conduit tioned second embodiment of the invention may be carried out. The stripping tower I0 is of the same general construction as the tower illustrated in Figure 1, but in this embodiment means are provided for introducing the ore tailings pulp separately from the recycled ore slurry. A sep- 1 arate conduit 22 is provided for introducing the ore tailings pulp at the top of the tower I0. A conduit 23 for the recycled ore slurry is connected with the tower l0 and discharges upon one of the intermediate plates, I l, which isnear the top .v

of the tower, whereby the ore slurry mixes with the ore tailings pulp before the same has reached a temperature at which the magnesium com,- pounds begin to hydrolyze (before it has reached about 150 F.). A branch conduit 24 is connectconduit 23.

With reference to Figure 3, there is illustrated an apparatus in which the third and preferred embodiment of the invention may be carried out and in which also a modified process hereinafter described may be conducted. In this embodiment there is provided an auxiliary heating tower 25 having therein a series of conventional plates 26 (the dish tray type being preferred) and having connected to the top thereof a conduit 21 for the introduction of ore tailings pulp containing ammonia to be recovered, a conduit 28 for the introduction of recycled ore slurry and anoutlet conduit 29 for the ammonia vapors and spent vapor. t the bottom of the heating tower 25, there is provided a discharge conduit 3U connect- `ed to a retention tank l1. Near the bottom of the tower 25 there is provided an inlet conduit 3i connected to the ammonia vapor outlet conduit i3 of the stripping tower l0, which tower `may be of the same construction as the tower illustrated in Figure 1.

The retention tank l'l is provided with an outlet conduit 32 connected to the inlet conduit I2 leading to the top of the ammonia stripping column l0. The said tank is also provided with an outlet conduit 20 for the ore slurry to be recycled which is connected through the pump. 2l to the inlet conduit 28.

In hereinbefore mentioned modification of the preferred embodiment of the invention, rthe heating of the mixture of ore tailings pulp and recycled ore slurry in the heating tower 25 is accomplished through the introduction of live steam into the bottom of said tower. In this case the ammonia gases and waste steam or vapor from the ammonia stripping column is led directly to the ammonia recovery system. With reference to Figure 3 of the drawing, this modified process may be carried out by the introduction of steam into a valved conduit 33 shown connected to the conduit 3|, leading to the bottom of the heating tower 25. The ammonia gases and waste steam in this instance are withdrawn through the valved conduit 34 connected to the conduit i3, leading from the top of the ammonia stripping column I0.

It should be understood that the third embodiment of the invention and the ,modification thereof just described may be partially merged and that the apparatus illustrated in Figure 3 may be operated to accomplish thechange. In the combined process, the heat supply for the heating tower 25 is provided in part 'bythe ammonia and vapor gases passing through the confed through the pump 2 I, to the recycled ore slurry kGli duit 3| and in part by, steam introduced through l the Vconduit 33. Under this operation, none of the ammonia gasand waste vapor need be withdrawn through the conduit 34. `In a nal embodiment of the invention operable under vspecial circumstances as where the Vsoluble magnesium content of the ammoniacontaining -ore tailings pulp is not too high, the

`recovery ofthe ammonia without excessive mag,-

nesium deposition on the plates of the ammoniastripping column or any `other equipment is accomplished by a modification of the first embodiment herein described, in which modification ore recycling is: omitted by closing ythe valved ,conduit I6' in Figure 1.

tion tank l1 to a temperature and for a period which causes the magnesium compounds to precipitate. out and to deposit on the ore particles, agitating to vpreventsettling and deposition of the precipitate in the tank, and passing the heat treated pulp to the stripping tower l0.

,It should be further understood that the present invention is not limited to the exact procedures or conditions described above or to the specific apparatus illustrated in the drawing, but that it covers all equivalents which will occur to those skilled in the art upon consideration of the general objectives herein described and of the claims appended hereto.

We claim:

, .1. A method for recovering ammonia by distillation from nickeliferous ore tailings pulp containing residual arnmoniacal leach solution and unstable magnesium compounds as impurities, whichpulp and impurities have a tendency to form deposits on hotheating surfaces at theammonia distillation temperatures employed comprisingheating said pulp by adding hot ore tailings slurryfsubstantially free of magnesium impurities having such tendency and by direct heat transfer from a IlOt fluid medium from atemperature below 150 F. to a temperature at which precipita- .tion of said magnesium impurities occurs, until `this precipitationhas been completed to an eX- tent substantially overcoming the deposition tendency, land evaporating ammonia from the pulp while the same is flowing through a plate distillation column.

v2. A method for recovering ammonia by distil- `lation from nickeliferous ore tailings pulp containing residual ammoniacal leach solution and unstable magnesium compounds as impurities, whichV pulp and impurities have a tendency to `form deposits on hot heating surfaces at the ammonia distillation temperatures employed comprising, adding to said pulp ore tailings slurry substantially free of magnesium impurities having such tendency, heating the mixture by direct heat transfer from a hot fluid mediumA from a temperature below 150 F. to a temperature Yat vwhich precipitation of the magnesium impurities occurs, maintaining the mixture in heated condition until the precipitation of such impuri- -ties h'as proceeded to an extent substantially formideposits vonfhotrheating surfaces at thenm- :monia distillation gtemperatures employed' 'Icomlprising, heating said vpulp 'by fmeans of. :alhot iluid medium mixed with.saidpulp, from a temperature below 150 F. to va'.-temperature at'which the magnesium impurities precipitate, .retaining 'the 'heated mass 'until the said :magnesium impurities have precipitated to an extentsubstantially overcoming the deposition tendency, then introducing` the treated pulp obtained intov a :plate distillation column and evaporating `.the;amrn :oriia -from the pulp/in said column.

'4. A method for recovering ammonia by distillation from nickeliierous Yore tailings pulp containing residual ammoniacal leach solution vand unstable magnesium compounds as impurities, which pulp and impurities have a ftendency to formdeposits on hotfheating'surfaces atthe-'am- Vmonia distillation temperatures employed comprising, adding to said pulp when thesame is ata temperature below 150 F. hot recycled' ore tailings slurry substantially freed of magnesium impurities having such tendency, further-heating-theresulting mixture -in a plate tower by'direct heat transfer with a gaseous medium toa temperature at which the magnesium impurities present rprecipitate, continuing the heating until said impurities have precipitated and lost'thisdeposition tendency, and distilling ammonia from the mixture in a platedistillation column ammonia-from the mixture in a plate distillation column.

5. A method for recovering ammonia by distillation from nickeliferous ore tailings pulp con- -taining residual ammoniacal leach solution and unstable magnesium compounds as impurities,

form deposits on hot heating-surfacesat the ammonia distillation temperatures employed comprising, heating a body of said pulp by=direct con-- .tact with live steam 'from a'temperature'below 150 F. to a temperature at which precipitation of magnesium impurities occurs until vthis precipitation has been completed'to an extent substantially overcoming the deposition tendency, .then passing the treated pulp'into and through a plate distillation 'column and therein evaporating ammonia from thepulp.

6. A method for recovering ammonia by-dis- :tillation fromnickeliferous ore tailings pulp containing residual ammoniacal vleach solution 4and unstable magnesium Acompounds fas impurities, which pulp and impurities have a tendency to form .deposits on'hotheating surfacesiat the ammonia distillation temperatures employedcomprising, adding to abodyof said pulp hotrecycled ore tailings slurry substantially .freed of magnesium impurities .having such tendency, steam heating the 4resulting mixture by -direc't heat vtransfer from a temperatureibelow .1`50`-F.to a temperature at which the magnesium impurities precipitate, agitating :the v'mixture to-prevent `settling, continuing the heatinguntil the precipitation of the magnesium impurities '-'ha's been completed to anextent substantiallyfovercoming the deposition tendency, .flowing the thusheated mixture through aplate column Iand evaporating oil? the ammonia from thesamewhile it is iin -said column.

r1. A method vfor recovering ammoniaby distillation from nickeliferous ore tailings pulpfcon- .taining residual ammoniacal: leach solution and ,unstable magnesium compounds. I as` impurities, which pulp and Yimpurities have a 4tendency -to form deposits on hot y heating.: surfaces 'at-the am- .fmonia distillation :temperaturesvemployed vcom- 135 which pulp and impurities Vhave a tendency to fprising., introducing -said pulp ninto ,the vtop of a plate distillation column, flowing the same ycountercurrent toa supply of steam, adding to said pulp in the column when the same is at a temperature :below 1150"' F. hot recycled ore tailings slurry substantially freed of magnesium impurities having such tendency thereby heating the pulp-'toa temperature which causes deposition as the heatingcontinues of magnesium impurities -on ore particles in the resulting mixture instead-'ofon 'the plates of said column, raising the temperature lof said mixture in the column toa degree -at which the ammonia evaporates and ftherein-distilling oi the ammonia.

8'. yA method for recovering ammonia by distillation from nickeliferous ore tailings pulp containing residual ammoniacal leach solution and vunstable magnesium compounds as impurities,

which pulp and impurities have a tendency to formdeposits on hot-heating surfaces at the am- `monia distillation temperatures employed comprising, adding to said pulp hot recycled ore tailvings slurry substantially freed of magnesium impurities having such tendency, heating the resulting mixture in a plate tower by contacting the same with a gaseous heating medium from a temperature below '150 F. to a temperature at which the magnesium impurities precipitate, retaining the resulting hot mixture during agitation until the precipitation of said magnesium impuri- -ties has proceeded to an extent substantially. overcoming the deposition tendency and finally passing the resulting mixture through a plate distillation )column and therein evaporating ammonia from the pulp.

9. A method for recovering ammonia by distillation from nickeliferous ore tailings pulp containing residual ammoniacal leach solution and unstable magnesium, compounds as impurities, which pulp and impurities have a tendency to -form deposits on hot heating surfaces at the ammonia distillation temperatures employed comprising, adding to said pulp hot recycled ore tailings slurry substantially freed of magnesium im- `puritiesrhaving such tendency, heating the resulting mixture in a plate tower by contacting the same :With'hot ammonia gas and water vapor cbltaned by the evaporation step hereinafter described,-the mixture being thereby heated from a temperature Vbelow F. to a temperature which precipitates the magnesium impurities7 retaining and agitating the resulting heated mixture until precipitation of said magnesium impurities has proceededlto an extent substantially overcoming vfthe deposition tendency, thereafter passing the treated pulp into and through a plate distillation column .incontact with live steam and therein evaporatingammonia from the mixture and producingthe mixture of hot ammonia gas and water vapor'employed in the first heating step specied herein.

110. A .method for recovering ammonia by distillation from nickeliferous ore tailings pulp con- .tainingresidual ammoniacal leach solution and unstable magnesium compounds as impurities, Whichpulp and impurities have a tendency to form deposits on hot heating surfaces at the ammonia distillation temperatures employed comprising, vadding to saidpulp hot recycled ore tailings slurry substantially freed of magnesium impurities .having such tendency, passing the resulting mixturezthrough a heating tower having dish-tray type plates therein in contact with steam and Withhot ammonia gas flowing from an ammonia stripping plate column, raising the temperature of the mixture in the said heating tower from a, point below 150 F. to a temperature at which precipitation of the magnesium impurities commences, maintaining the mixture in heated condition until precipitation of said magnesium impurities in the pulp has been completed to an extent substantially overcoming said deposition tendency, passing the mixture through said ammonja stripping plate column wherein ammonia is evaporated off through direct steam heat applied to the mixture and whereby substantial deposition of magnesium impurities and ore particles upon the plates in the ammonia stripping tower is avoided.

ROBERT R. FITZHUGH.

BENJAMIN F. FREDERICK.

BERNARD A. AXELRAD.

REFERENCES CITED The following references are of record in the le of this patent:

World Engineering Congress, Tokyo 1929 Proceedings, vol. 35, Mining and Metallurgy, part 3 (Non-ferrous Metallurgy land Ore Dressing); edited and published by World Engineering Congress; distributed by Kagakkar Marunonchi,

20 Tokyo, 1931, pages 217-235. 

